Groin of variable permeability and a constructional unit therefor



March 25, 1958 E, T. HUNTER 2,827,769

GROIN OF VAR LE FERMEABILITY AND A CONSTRUC NAL UNIT THEREFOR Filed Oct. 18, 1954 3 Sheets-Sheet 1 INVENTOR mam-:0 1'. HUNTER ATTORNEY-5 E. T. HUNTER GROIN OF VARIABLE PERMEABILITY AND A CONSTRUCTIONAL UNIT THEREFOR March 25, 1958 Filed Oct. 18 1954 5 Sheets-Sheet 2 INVENTOR ELDRED T. HUNTER ATTORNEYS March 25, 1958 E. T. HUNTER GROIN OF VARIABLE PERMEIABILITY AND A CONSTRUCTIONAL UNIT THEREFOR 3 Sheets-Sheet 3 Filed Oct. 18, 19 54 INVENTOR HUNTER ELDRED ATTORNEY$ United States Patent GROlN OF VARIABLE PERMEABILITY AND A CONSTRUCTIONAL UNIT THEREFOR Eldred Tait Hunter, Jamaica, British West Indies Application October 18, 1954, Serial No. 462,950

20 Claims. (Cl. 61-4) The present invention relates broadly to the art of erosion control of beaches.

More particularly this invention relates to a groin for use in stabilizing beaches by controlling erosion.

The invention is particularly directed to a groin of the permeable type.

The study of the effect of waves, and ocean currents has developed to the point where numerous attempts have been made to control erosion of beaches by inter-, cepting the littoral drift so as to deposit materials contained in the littoral drift onto the immediate beach in a controlled manner. The groins that have been constructed before are both impermeable, that is solid structures which do not allow water to pass therethrough, or in some instances permeable, which do allow for the passage ofwater. Accordingly, this invention is particularly directed to the latter type or permeable groin and has for one object to provide an improved permeable groin that is economic to manufacture, readily erectible, stable in situ and one which will automatically conform itself to the profile contour from the shore outwards, and which groin is constructed of a plurality of units so inter-related and assembled as to permit lateral or vertical shifting among the units to ensure that the groin is stabilized.

It is a particular object of the invention to provide an improved groin in which the individual units are so inter-related that they can move relative to one another laterally and vertically to a suflicient degree as will ensure stabilization and compensate or cushion the effect of lateral or quartering wave shocks.

It is a specific object of this invention to provide an improved structural unit for use in assembling groins and which unit is a plate-like element having one or more apertures therein at different vertical heights and having plural spacer means projecting from one face thereof at different vertical heights and includes means embodied with the spacer means whereby when successive units are arranged adjacent to one another the last mentioned means of one unit loosely engages within the apertures of the adjacent unit. From one specific standpoint, the invention comprehends a unit of cast concrete, preferably prestressed concrete that has integral spacers projecting from one face thereof and groups of apertures extending through the structure above the respective spacers, the spacers having projections on their outer faces that are cooperable with the apertures of the succeeding unit and which projections function as guides to facilitate assembly of the units and as retaining means to limit the degree of lateral and vertical deviation of one unit relative to another.

As a further specific object the invention comprehends a variable permeable groin constructed of a plurality of plate-like units spaced from one another in the direction of the extent of the groin and each unit disposed at an angle to the shore profile. In other words the several plate-like elements are mounted in what may be termed a rearwardly inclined position and include a base spacer A 2,822,769 Patented Mar. 25, l ii 'ice extending perpendicular to the angle of incline so as to present in cross section a substantial V-shaped bottom to a vertical load which facilitates settling of the several units and provides a stable base even in shifting media such as muck.

While this invention is primarily directed to the provision of a permeable groin, it is a further specific object to provide an economically constructed impermeable groin.

.Further and more specific objects will be apparent from the following description taken in connection with the accompanying drawings, in which:

Figure 1 is a sectional view through a sea beach having a gently sloping off shore profile and illustrating a groin embodying the invention after having been erected thereon,

Figure 2 is a view similar to Figure l but illustrating a groin constructed on a sea beach having a more irregular off shore profile.

- Figure 3 is a perspective view of a unit for use in constructing thegroin illustrated in Figures 1 and 2 and diagrammatically illustrating the enlargement of a unit to suit irregularities in an off shore profile,

; Figure 4 is a front elevational view of a modified form of groin unit,

groin of the type agrcin constructed of the units shown in Figure 4 and further fragmentarily illustrating the stages of applying a :top cap to the groin, V

Figure 8 is a fragmentary, vertical cross sectional view illustrating the top portions of the two adjacent units of the type shown in Figure 3 when embodied in a groin,

Figure 9 is a perspective view of a groin unit of the type shown in Figure 4 modified to constitute part of a groin that is substantially impermeable, and

'Figure 10 is a cross sectional view taken on lines 16-40 of Figure 9.

The permeable groin of the present invention is constructed so that the degree of permeability is increased from bottom to top as desired. The constructional arra'ngement however includes a disposition of weight with respect to the vertical dimensions of each unit such that the center of gravity is below the median center line re sulting in the units having a tendency to fall over backwards if deviated slightly from the vertical in the direction away from the side from which the spacers project. Essentially the unit has a cross section of a ribbed slab. Preferably the plan of each unit is of truncated formation, that is, it is much wider at the base than at the top. It is not absolutely essential that the tops be flat since a triangular shape in plan is effective. The shape essentials comprise upwardly converging sides. This shape has proven effective and dispite the absence of piling or other supports or base structures, a groin constructed in accordance with the invention adequately resists wave shock directed to the sides of the groin that is the effect of lateral or quartering waves.

The units of the groin may have different heights which is governed by the slope of the bottom or off shore profile. For a gently sloping profile as in Figure l the units would all be of substantially the same height and the top line of the groin would slope more or less parallel to the line of slope of the bottom. The fact that the groin is permeable provides a variable control as regards interception of littoral drift.

It is further to be pointed out that in the majority of instances the present invention is utilized to construct a groin field, that is, there will be a plurality of groins V tance sufiicient to r an s, p t nn aps. Thiseud: block (3 is similarein Priecting o nt h w ter, eneral n Paralleli m with one another. This of course is the desirable aspect of a beach erosion control system on a large scale and w p n i a P e t How e en, he. pre e invention P I Q o a w we? readil ma pul tablc unit n struction ideally suited for; purghase; by indilvidualstownr in g beach pr ope'rty andparchaseby-bcmh; controlhoards in municipalities and the like, to answer immediatetheach;

ture p r =i ferably cast: block; B of; prestressed'. concrete, however it is. possible to assemble the groin units A= inextensior ot a;rock formation "The base blocleprovides a it ble; il i l, a utment: 1 the Severalunits are then positioned in sequence to extend seaward: from the baseblock. When. the groin extended: seaward: a ,dis-

' terpept thelittoral drift anendiblock P the P s i hq t itst t Each unittin tp me ns metasta le. hi ueceeding ni s: to restrain; e unit from outward. movement. The units andigroinslib lustratecl: in; the drawitigs ara CQ1JH1lCtdOfE prestressed concrete, however the invention is not to be limited: to the structural material; used; sinceany; material suitable for the purpose can be employed. Thfl grpinstofsliigures 1vandlt re un tmctedzq u itstsh i n Figure The nitt t udest n t z q ase rt un Liliana-prov e tha hre t nsy s ly:ex euslm tsp ee s .1 andii The'ribt 4 constitutes a foot for 'thebaseportiom T he p ceribiz xts dr t mqnee aeez ly di and i bv t Di u e/ri al y'q aper r s t ha-t fixtendhe et l The p tureshayeigreater crosgsectional area thanthe projection.

5 so that whenthe. sucpe ssive units are assembledin the manner shown-in lfigu res l andZ the; projections fit loose- 1y within the apertures whereby one unit'ca-nmove vertil y d te l l la iv etheadiaccnt uni n h freedom of movern m ment Qfu relative to another, is-'; permitted;

ure '3 vdi g amniatia lr ll s rates n-s nlar m n of the units Af'of Eigure 21in the unit utilized to proyide instances where the off sh ore profilei Irregular The.

larger sizetunit will have an e QIEm IQ ribs-4'41! addition to the previous ribs 2, 3 ,and 4. V

The 'units illustrated indicate the essential features: of

the invention, howeverfihey arenot drawn to the precise proportions since th e siz e of; th e spacingmeans and pro-t jection and the over-all size and thicltness of the plate: units can be varied in accordancewith conditions. In the practical embodimentconstructed of prestressed concrete, the base member is nine feetfromltopto bottom, has its sides upwardly converging irom abase widthof' eight feet,- and the. ribs 2 3;angl 4-elgtend outward frorn one face of the basev a distance approximately twelve inches. These ribs are approximately-nine inchesthich and the projections 5 will thushaveapprqximately, nineinch vertical-dimensions and aresigtinches wide; The apertures 6 throughthe base are approximately-twenty,- seven inches in verticaldimensiqn-and nine inches;wide.

There is an aperture fijthrough the base j-for1-each pro1 jection, extending. from the ribs; and; the apertures are vertically aligned with the projections so-lthat jwhen-one unit is placed against the next he aperture sqoi the said one:

unit fit loosely over the projections on the precedingiunit. The difference indiinensions between-v the projectionsiand th p ejections; 5i, extendaoutwardly Further the: base; 1; is. provided with a; plu-t is such, that a. slight swinging mantr s.

hitt aterally; y three, inhe s-.. The, bottom of theunit or base presents a surface that is eight feet wide. Where the base is constructed to be approximately three inches thick, a bearing foot at the bottom of the unit having approximately a fifteen-inch width will result. The total weight of the unit is approximately 3,000 pounds and the foot dimensions of eight feet by; fifteen inches provides 'approximately ten, square feet of, base area. for bearing against he a tq nt A-un t w igh n QMOQpounds having a ten-square-foot base area can be supported by a 300- pound per square; foutlunderlying base material; Thus units Q his, p an a suup t d n m sk, Since; the groin ofFigure's' 1" and2- is permeable the material in the littoral drift inypassing throughtthe, groin will be deposited hydraulically so that the strength of the bottom or underlying base material will be increased.

it is further to be pointed out that the sliding movent Qt he un s; n lat ye tow onetanother'faeilitate their adjusting themselves to the slope Ofz-thQOfi shore'profilel and; irregularitiesg in the shore, and; underwater.- base materials As ndicated the inyention contemplates construction of diiferent size units insofar as the vertical; and. base idth; dimenaiqnsare oneemed: However. the angle; of slop of; thetsideswillbelthe same. 'Ihusdn. certain C0317. t bns 3S; shdwninli gurel; agroin will'zrequire aucer taintnurnbert ofismall sivzeun-its A andtthen if. the-offshore pl fikthasaam abrupt dip therein: it willbe necessaryto ins rt severah'larger: unitstAf-int place.. The length: of:-'theunits,totbe usediiadetermined by. the: length ofsthegroin, theangle: ofzslepe qfsthe-olffshore profile-and the-desired angle of: slopeitotbe=built up byiuse ofe the groin.- Hielength o'f'; theagroirttmnst be suchithatcit will intercept the littutal'qdrift it: being understood: that thelittoraldrift QWSi oifz shore and: p'arallelzto: the shore iAszstated l-"ziguregsli illustrates an embodiment inwhich the off: shore profile: can betel-med: gently'sloping and all of thegroin-tunits-Ai are-"identical: The groin isbuilt up apertures result in an arrangcmflnt Tin which-tonetunit canfrom. the: base; blbCiQ'B? which: will beconstructed of concreteiintar stabilized area; of the beach; The outer faceofathes-block B isislopedrat an angle of: approximately and during the formation of the block, spacer means such as; ribs R areiformed= that eirtend'across-the face of low whereby'tliegrains have a normal tendency to fall;

backwards if deviated from thwertical in the direction away from the spacer ribs. Knowing the angle ofslppe of -the off shore profile the groin in Figure 1 after the base blockB'has been constructed in situiis readily assembled'bythe use of a mobile crane. The indiyidual groin.units weighapproximately 3,000 poupdswhencon: structed' ofprestressed' concrete Suitable lifting books such asafiS-are provided for liiting up eachunit The unit is swung out flowered inplace adjacent the bottom 7 of the sloped portionof the base blqck andftheuvis'low ered back at the 'angle-ofi thebaseblock Since the open-t,

ings;in thefirs t'unit: are longer in .the vertical dimension than the vertical length of the projections on the base block, the first unitcain slide downwards untilits base is stabilized} A ter hevfiri t nit is pla ed e a e k; e rei qj i hat nq tmds tehm e r i h r l o a all $9. as i s) v teyen tba kwash t of f-the water or wayes trom moving thel unit seaward, of bass Elgcknd.andt uh auuentuni e r similarly loweredin place with the ibars7, being bent over I to prevent outwardniovenint of'thc units relative to one another. As indicated previously the larger area of the apertures 6 when compared with the cross sectional area of the projections 5 permits each unit to have movement relative to the adjacent unit both vertically and laterally 'to a certain extent until the units adjust themselves and are stabilized. This mobility of units relative to one another is further important to minimize the shock of quartering waves.

After the number of units have been assembled in place so as to extend the groin seaward the required distance, an end cap C is lowered in place. The end cap is fiat on boht faces, has the same plan shape as the other units and has apertures 9 therein that are made with reasonable close tolerance as compared with the cross sectional shape of the projections 5. The steel bolts or rods 7 are deformed to hold the cap in position. The cap presents an inclined face to head-on waves. As is clear from Figure l, the permeability of the grain increases variably from bottom to top and in the course of time the material accompanying the littoral drift and the material of the sea bottom will fill the spaces within the groin and eposit material on both sides thereof.

Figure 6 illustrates in perspective, a suitable groin and indicates the action of quartering waves as regards the shape of the groin. As noted, each groin panel unit A has an inclined side 10, thus a quartering wave moving in the direction of the arrow W will strike the edge of each panel as at 11 so that the water flow is split to pass across the face of each panel and rearwardly thereof to strike the face of the adjacent panel where again the flow is split from flowing through the groin. This action mininLzes the shock effect of a quartering wave. Further since the base panel when made of prestressed concrete has a certain amount of flexibility, it can deflect under shock to a limited degree and still return to normal shape without cracking and exposing the embedded steel components. Utilizing prestressed or high strength concrete in constructing the panel units minimizes the abrasive effect resulting from wave action.

The units utilized in constructing the groin of Figure 6 are shown in Figure 3. In plan, the truncated arrangement includes sloping sides and projecting from the outer exposed face are the spacer ribs 2, 3 and 4 with the projection 5 thereon. The apertures 6 are so arranged in each unit that the projections of the adjacent unit loosely fit therein. In this form the unit is closed on its top and subjacent the top edge is a single aperture. The figure further illustrates diagrammatically and in dotted lines an enlarged unit insofar'as vertical and base dimensions are concerned. The angle of slope of the sides is the same and the outward projection of the spacer ribs and projections remains the same although the ribs are of course wider due to the increased base width at the bottom of the unit. It is further noted that the center of gravity of an enlarged unit remains below the transverse median line of the unit so that the unit is very stable and would have a normal tendency when tipped to stay in that position resting on the'sloped face.

Figure 7 illustrates in perspective, a groin constructed from the modified form of panel unit shown in Figures 4 and 5. In these latter figures, the unit includes the base plate 13 of suitable thickness as regards strength. Projecting from one face of this plate are spacer ribs 14, 15 and 16. Each spacer rib has one or more projections 17 extending therefrom and steel bars Or rods 18 project outwardly from the face of the projections. The side edges of at least the top spacer ribs are sloped as at 19 and rows of apertures 20 are provided in the base plate for cooperation with the projections on the ribs 14 and 15 of the preceding base plate. At the top of the base plate in this modification, there is an elongated notch having inclined sides 21. This notch as shown in Figure 7'is utilized when the groin is to have a concrete top cap. In Figure 7, the units nearest adjacent the base block B present an appearance in which the notches 21 of the suc-'- ceeding units are in alignment. To construct the top cap, wooden forms 22 are fastened to the sides of the groin, it being understood that these forms extend from end to end of the groin and the area between the wooden forms 22 is filled with concrete as at 23. If desired, suitable reinforcing rods as at 24 can be laid in the notches. The top cap when set provides an arrangement in which each panel unit in effect fits in a slot in the concrete of the top cap which means that the plates are restrained but not firmly fixed whereby settling and slight lateral movement is still possible. The inclination of the walls of the notch facilitates this slight lateral movement. The incline 19 on each side edge of each top spacer permits laying the form boards 22 flush against the sides of succeeding spacers. In placing the form boards 22, a cover is placed under the notches 21 so as to prevent the concrete flowing down into the space underlying the top spacer 14.

It is believed that the construction of a groin utilizing the present invention is clear from the drawings, in that with the formation of the base block the individual units are positioned in place, the bars or rods as at 18 are deformed between the positioning of succeeding units and an end cap as at C is placed on the end. The concrete top cap is formed after the groin has been built to the length required.

The wooden forms 22 are so arranged that the concrete' 23 of the top cap does not extend below the top spacer 14. The base block B is provided with a notch as at 21' so as to securely anchor the inner end of the concrete top cap. The end plate C as stated previously,

is flat and has apertures formed therein to closely conform to the dimensions of the projection 17.

Figure 8 illustrates in cross section the relation of the vertically elongated apertures 6 to the projections 5. As shown, the apertures both in the forms of Figures 3 and 4 extend from just above the level of the respective spacer ribs upwardly and in number corresponding to the number of projections. Only one restraining bar or rod respectively at 7 or 18 has been illustrated as extending from each projection. Obviously two or more such rods can be bent over in the manner as shown in the drawings to restrain the respective units against outward movement.

It is to be specifically pointed out that the invention is not to be limited to an arrangement where all of the spacing means constitute ribs extending completely across one face of the panel. It is necessary that the bottom spacing means as at 4 and 16 extend completely across the face of the panel so that in cross section the bottom portion of the panel is L-shaped and provides the required base or foot area. However, the intermediate spacing means such as at 2 and 3 do not have to be complete ribs. Ribs are desirable but the invention contemplates an arrangement in which individual projections extend from one face of the panel in the intermediate areas at least which are shouldered to provide the reduced area necessary for the projections 5 that engage in the apertures 6. Where a top cap is to be used, the top spacing means is a rib extending transversely across the face of the panel.

Further the units utilized in constructing the groins in Figures 6 and 7 readily lend themselves to modification to construct a groin that is substantially impermeable. Figures 9 and 10 illustrate such a modified groin unit. The unit is the same as that shown in Figures 4 and 5 with the exception of the vertical ribs 25 that extend between the bottom spacing rib 16 and intermediate rib 15 and also between the top of rib 15 and the undersurface of rib 14. One vertical rib is in the upper portion of the unit and the vertical rib 25 between spacing ribs 15 and 16 can be positioned between either two of the three apertures. A groin constructed of a unit illustrated in Figure 9 is still able to move the required amount vertically and laterallyto ensure proper stabilizationbut is substantially impermeable since the... vertical I'ihSf "25; ci h' nimpe edl an. age or wat r ihr'ough. the spaces,- et een i jasent ni nihfi teral directi n} The. nv ntiq iprovid s a wide range of. con tiiuctional. methods. The vertical heightof groinunits will o'f course e. dete mined; by he: n sh re. e otIQm. andifiens heg bi co tructed. ofl a ard zedl nit ranysunble t uctural. material su h asf-ii e 'tres ei on rete, re nl q eicbnc ete, steel mber. "The mn e e sr 1. panel. nit n ludin space s. and pr jectio c n; b molded in agsingle operation 'from'cpncrete materialsor. f. esired. he p ers. w t lhe'i nrci tionsecan be made epara e y. and'eit i n bb ted o Pr fo med a k: pane s. embedded b e mw ii he ackn nels arel e ngmn QbYiQ llY- evaribus omponen s. Wh b'maded timbe ll. bebb ted. bs t nd nt j ced as-ne e 'sa y Ibe Pane s. of tbe;.i v. n 9n.c n. c nsfmctbdo steel f desired. In other'words,*this invention is not to;he,lim eslfioz heu eof any. parbicula s ruc ural ma e al be n rne in min ha r ga dle s, of. he SiIl S filral ma er a utilized the-individual units have the sarnefiharaeteristics, am y aplate-like b panel aving ap rtu she in. at, different levelsi'n the vertieal dimension and between the aperturesa plurality of. transverselyextending spacer b ha ing, pr je ion xte di he efrom o size smaller than the size of the apertures whereby panels'c an be su ce sively place b e p h ther he ap r s Q one p ne f o ely ttin ov r. he Pr je t n bep e eding pane andl e ackfface h one pane ng g n he pac fi hep ed nspan l- M an a proyided to restrain outward moyernent of. thesaid one. Pa el lative to th p e fiinsp h The invention is not, tofbe. limited. to a truncated v shape but, the outer margins of each panel are preferably inclined toward theflop, In other words, the panels. are of imini hing width toward t topt o ours P $Sib16 o bo r t be pa s th; curved dge n other words, the groin as. Constructed presents. a receding ace n the path off cvemen f w v rorn y d r t on- It. is to be further borne in mind that thepanelscan befabribatcd in situwhere the groin islto be constructed.

or made up ina factory in units and transported to the e. There o e he. pres ven i np o d s g o n ruc ed oipane jwh bh' p f bly are truncated iangular sloped, withvariably fixed and spaced spacers and apertures so that whenerected, a, non rigid solidly sedbr i l ted prism is P o a i Slopes o eease nc min ve o e and With the pane t ed. o resi t u oin a e q' es e eby, co stitute a variably permeable groin to control the depositof solids carried in' the littoral drift and thus assist formation of beaches and preserve beaches along shorelines,

s p i e tp ev usly, he d vidua p el ha movement relative to one another so that the groin can adjust itself Within limits to the underlying base material n a s n l pe o he h reprcfi e In keeping with the design of permeable groins the space between the toptwo spacer ribs isgreater than at. tw en. he. nde y n i s SQ ha permeabilit variably decreases toward the bottom of the Panel of e o n to P de great nter e nce to littor l drift at the-bottom as shore material builds upthe in. creased permeability at the top allows. free distribution of solids ,on both sides of the groin;

' It is to be further pointed out that changein offshore profile s pe. can n e t y ncreas ng. o de-v creasingthe outward extentof thespacers proportionately from top to bottom, in other words, support one panel furthe r.- away from the. preceding paneltat the topthan .70 atthe bottom so .that-thesaidione panel hasamore stable angle. As previously indicated LfOP- large changes inprofile s'lope the-size' of-the panelis. increased proportionately; and meets-the slope conditional if conditions require-greater orless: permeability in-the groin thespacer aspires bsc n e npcrea ed' n r sed n e sb n r dth I resnectively asd s redg Y r r 'lty s tp be snecifi... v11y,minted.bu .tha ars bl n can: structed; in accordance with. h present. n ntion. ot equ e he se .n l ng many o er u de -remai s, onsequently he me requi ed. o re t, afsrb i rel: ducedto a minimum so that installation cost is materially r duc d. Where be re ns. re n truc e o pan u i pr st sed concrete or. hi h tres ed n e h h is resistant'to abrasion, the; life off'the groin is materially n se an m in enan o t arejr duc d o a minimum. i

Wha is blaimedis; 1 A tQ r qmnr sin a s s. o ont uou emb rs. 15 c h v n l t .b.q upw y co v n ides. and 'spaceprneans at tlifi ent levelsabove thejioot, said me rs. e n p iti d o ex e d e w rd n r a rd y, n ned 's uentiah, pa al e sp e e a bnw at a t 'P P QH of -he p cer m ans'and. a fo f 0 one unit engaging. the succeeding unit.

2'. A groin comprising a -plur lity of units positioned in rearwardly inclined setnlent'ia1 relation, each unit .including spacing means projecting from one face only, said spacing means including shoulders extending sub v stantially parallel tothe plane of said; face and :projections extending outwardly ofthe shoulders, each 7 further having apertures therein and the projections of one unit beingdisposedin the apertures ofa succeeding unit 'and* the shoulders engaging; with the opposite face of a succeeding unit to 'space the units in substantial parallelism wherebythe groin is permeable and means preventing the units from outwarddisassociation relative toone another.

3; A groin asclaimedin claim 2', including upwardly converging sides and the shouldersincludinga n'b projecting from the hase'of'each unit and extending transversely across the same *to constitutea: lateral foot at the bottom of each unit'andsaid projectionsinclnding plural projections eggtending outwardly ofsaid rib. i

4: A groin as claimedin claim} in which the aperturescorrespondin; number to the number of projections and are larger in two; directions at right angles to one another than the projections thereby permitting lateral and vertical movement of one-unit relative to another.

5. A groin comprising a series of units positioned in. sequence to extend seaward; each unit comprising a base plate having upwardly converging sides, a plurality of spaced ribs extending across one face only .of the plate including a ribat the bottom of each unit, projections 5 extending outwardly of the ribs and the base plate havingapertures theret-hrough in number corresponding to the projectionsand offset vertically therefrom whereby the aperturesof succeeding units fit over the projections of the-preceding units with each unit being upwardly and 'rear-wardlyinclined and having its rear face spaced from the base plateof the preceding unit,

6. A- groin as.- claimed in claim 5' in which the aper-' tures have greaterdimensions in two directions at right GO angles to one another than thecor-responding dimensions laterally andvertically relative to one another.

7 .A- groinasclaimed'inclaim 6 inwhich; the; apertures are elongated 'vertically-to permit-substantial verticalmovernent of one unit rclat-ive toanother.

' 8. A groin as claimed in claim 5 and-a concrete cap poured: over 1116IOP$ of the units.

.9. A groinas; claimed in claim; 5 in which the grain isimpermeable and .includesverticalribs on each base P atex ndi g b tw en the ran ve e s- 9,- A .s bi ituni r u e naa semb insasrb sfi e n L b Watd Said. Tt bmn i'gsiabdy, pbrti m ave ns. a. bo tom; n upwardly,- con si idedges; pac: s mean embodi d w th the; r ntq e o y portio t fie en lev s nblitdinse petpe tlbn rte s tran 5} versely across the body at the bottom thereof, said spacing means further including projections at different levels above the foot portion, said unit further having apertures therein corresponding in number to the number of projections so that a plurality of units may be positioned in rearwardly inclined spaced relation with the projections of one unit within the apertures in a succeeding unit.

11. A groin unit as claimed in claim 10 and securing means carried by the projections and adapted to cooperate with a succeeding unit in assembling a groin.

12. A groin unit comprising a base plate having a plurality of spaced ribs extending transversely across one face only thereof, projections extending outwardly of the ribs and the base plate having apertures therethrough in number corresponding to the number of projections and which apertures are offset vertically from the ribs and vertically aligned with the projections.

13. A groin unit as claimed in claim 12 and deformable securing means carried by each projection for cooperation With a succeeding unit in assembling a groin.

14. A groin as claimed in claim and said apertures including an elongated notch extending inwardly from the top of the plate to the level of the upper rib.

15. A groin as claimed in claim 5 in which the opposite ends of each rib extend at angles inwardly toward one another.

16. A groin as claimed in claim 5 in which the space between the uppermost ribs is greater than that between the other ribs.

17. A groin unit comprising a base plate element having opposite faces, greater transverse dimensions than thickness and major and minor axes, plural spacer means extending outwardly from one face only and including free projecting ends and shoulders constituting supporting surfaces extending transversely of the plate and disposed between said face and said free ends, said spacer means being arranged at spaced areas along the major axis and said base plate having apertures therethrough corresponding in number to the number of projecting ends with the apertures offset from and in alignment with the projecting ends in the direction of the major axis whereby the apertures of a succeeding unit can fit over said projecting ends with the face of a succeeding unit engaging the supporting surfiaces.

18. A groin unit as claimed in claim 17 in which the spacer means comprise ribs xtending transversely across the plate in the direction of its minor axis and said projections extending outwardly from the ribs.

19. A groin as claimed in claim 18 in which one of said ribs extends across said plate along the bottom edge thereof when the plate is viewed from vertical position.

20. A groin unit as claimed in claim 17 in which said spacer means comprise n'bs extending transversely across said plates at different levels in the direction of the minor axis, said projections extending outwardly of said ribs and additional ribs extending parallel to the minor axis and between the transversely extending ribs at areas of the base plate displaced laterally from the apertures.

References Cited in the file of this patent UNITED STATES PATENTS 231,957 Dyer Sept. 7, 1880 1,179,121 McGillivray Apr. 11, 1916 1,812,300 Leeds et al June 30, 1931 2,159,685 Buzzell May 23, 1939 

